Amyloid beta (Abet) is the major constituent of the fibrils deposited into senile plaques and cerebral blood vessels of patients with Alzheimer's disease (AD). It is also normally present as a soluble component (sAbeta) in body fluids, in association with lipoprotein particles. Two apolipoproteins, apoE and apoJ , interact with Abeta peptides with high affinity. ApoE is mainly complexed to Abeta in amyloid deposits while apoJ seems to be a circulating carrier molecule for sAbeta. In addition, the blood brain barrier appears to modulate the uptake and clearance of sAbeta. The main hypothesis behind the project states that circulating soluble Abeta contributes to the formation of the fibrillar Abeta found deposited in senile plaques and vascular amyloid angiopathy in elderly individuals and AD patients. The overall goal of this proposal is to study the relationship between apolipoproteins and the Abeta pathogenesis in AD by investigating the role of both apoJ and apoE in the transport, cellular uptake and catabolism of sAbeta and its potential contribution to the deposited Abeta. We have planned our studies at three different levels (biochemical, cellular and in transgenic models) in close collaboration with the other projects. In specific aim 1 we hypothesized that the concentration of free sAbeta in body fluids is modulated by multiple factors. We plan to study the degree of peptide association with plasma and/or CSF lipoprotein particles, the differential interactions with apoJ and various isoforms of apoE as well as the potential occurrence of post-translational modifications associated with aging in elderly individuals and AD patients and compare with similar parameters obtained from normal young individuals. In specific aim 2 we hypothesize that specific cellular receptors mediate the interaction of sAbeta with cerebral endothelial cells, neurons and/or glial cells. Receptor dysfunction in elderly and AD individuals may provide a mechanism of increasing sAbeta concentration into the brain parenchymal. We propose to biochemically characterize sAbeta receptor(s) in primary cultures of human cerebral endothelial cells (from young and elderly individuals and AD patients), extend the studies to neurons and/or glial primary cultures of murine original, analyze potential differences in functionality and identify cellular sites of clearance and degradation.